packaging and meat quality

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Page 1: Packaging and Meat Quality

Packaging and Meat QualitySusan A. MullerLaboratory Services

Winpak Ltd.Winnipeg, MB R3j 3T3

IntroductionThe appropriate packaging of meat and meat

products can bestow a number of benefits. Extensionof quality can be achieved in a hermetic packagethrough exclusion of contamination, delay of microbialspoilage, maintenance of desirable color and minimi­zation of water loss. The extension of storage life makespossible a broader geographical distribution of thepackaged products. Other benefits include greater han­dling convenience and improved presentation toretailers.

However, these benefits are contingent upon the cor­rect selection of packaging materials and system. Forexample, there are currently two trains of thought inthe retail packaging of fresh beef:

One method is to vacuum package in a film verypermeable to oxygen allowing maximum possibleexposure of the meat surface to oxygen. This is basedon the concept of consumer preference for a bright redcolor. The red "bloom" color can also be achieved bygas flushing with an oxygen rich environment. Thedrawback is a very short shelf-life.

The second method is to vacuum package using avery high barrier film to achieve maximum quality andextension of shelf-life. However, this method requiresre-educating the consumer that purple (deoxygenatedmeat) is as good or better than red meat.

Whilst the variety of systems available increases theopportunity to find the ideal packaging system for agiven application, it also increases the possibility thatan inappropriate system will be selected unless themeat product requirements and the properties of thepackaging are fully understood.

Vacuum PackagingVacuum packaging refers to packaging in containers

(rigid or flexible), from which substantially all air hasbeen removed prior to final sealing of the container.This method of packaging is actually a form of "Modi­fied Atmosphere" since normal room air is removedfrom the package.

Advantages1. Extends shelf-life. Vacuum packaging aids in con­trolling oxidative rancidity and prevents the growth of

A presentation to the 31 st Annual Conference of the Canadian Insti­tute of Food Science and Technology, Winnipeg, 1988.

22/ AT

normal spoilage bacteria. Aerobic organisms such asPseudomonas are suspended and lactic-acid bacteriaare favored. Lactic acid bacteria cause a less offensivetype of spoilage, at higher bacterial numbers, thanother, aerobic organisms.

2. Reduces moisture loss & freezer burn. Vacuumpackaging prevents movement of water out of theproduct into the surrounding headspace. It also pre­vents loss of moisture at product surface and eliminatesfreezer burn.

3. Requires minimal storage space. The package isdraw tight around product taking up minimal space.

4. Leakers are easily detected. A small puncture orpinhole in a vacuum pack is easy to detect by lookingfor loose packages.

Gas PackagingGas packaging can be defined as the alteration of the

proportional volumes of the gases which comprise anormal atmosphere. This type of packaging generallyfalls into 2 categories.

Controlled Atmosphere (C.A.P.) refers to controlledsystem whereby gases are added or removed to main­tain a desired balance. In this case the bulk bin orstorage vessel is virtually impermeable. Modifiedatmosphere (M.A.P.) refers to enclosing a product insome type of barrier, and modifying the atmosphereeither by drawing a vacuum or filling with a gas mix.During storage the level of these gases will change dueto respiration of the product & permeability of the film.

Advantages1. Allows meat to bloom. A blend of gases incorporat­ing oxygen can be used to maintain the desired redcolor in fresh meat.2. Extends shelf life. Gas packaging controls oxida­tion by displacing the oxygen with carbon dioxide andnitrogen. This inhibits bacterial growth of normalaerobic spoilage organisms. The gas mix also aids inpreventing surface mold.3. Prevents crushing of soft products. Gas mixturesof carbon dioxide and nitrogen equalize the pressurein the package and prevents package collapse.4. Retains moisture. Gas packaging prevents theproduct from drying out by containing the moisture inthe package. However, water can move from center ofproduct to surface resulting in staling.

J. lnsi. Can. Sci. Technol. Alimem. Vol. 23. No. I. 1990

Page 2: Packaging and Meat Quality

NOTE: There are additional cost consideration in a gaspackaging system due to materials, equipment andlabor requirements.

Product Shelf-LifeProduct shelf life is ultimately controlled by 3 factors:

1. Product characteristics. This refers to the type ofproduct packaged (i.e. meat, fish, cheese, etc.) and themicrobial load upon packaging.2. Environment. The temperature and humidity towhich the product is exposed plays a key role in shelflife.3. Properties of the package. The package itself aidsin controlling the oxygen and moisture vapor transmis­sion rate.

It is important to note that packaging cannot improvethe quality of a product, it can only maintain its presentstate.

Fresh Meat Products

Red MeatsFresh meat requiring extended storage requires a gas

impermeable, air-tight package to prevent bacterialgrowth, excessive shrinkage and discoloration.

When vacuum packaged, residual oxygen is con­verted to carbon dioxide through the respiration of leantissues and microbial activity. This type of environmentseverely restricts the growth of common aerobicspoilage bacteria and favors facultative anerobic organ­ism such as "Lactic Acid bacteria".

If vacuum packaging procedures are followed cor­rectly, the storage life of meat is extended several weeksfrom packaging - typically 10 to 12 weeks for beefprimals. Vacuum packaged portion or retail cuts wouldhave a shelf-life of about 4 weeks provided a good oxy­gen barrier film is used.

PorkThe use of vacuum packaging to extend shelf-life has

not proved as successful with pork as it has been withbeef. One reason is the greater proportion of meat ofhigh pH (>6.0). The bacteria which grow on such meatcause spoilage much more rapidly than do lactic-acidbacteria which multiply on meat of nC?rmal pH. Undercommercial conditions chilled vacuum packaged porkhas a shelf-life of about 21 days.

The pH of the muscle and storage temperature playa key role in the shelf-life of pork. Normal pH porkstored at O°C usually spoils due to a flavour change.In contrast high pH pork often develops undesirablechanges in appearance as well as flavour and shelf-lifeis limited by the development of green color defects.When these packs are opened a smell of hydrogen sul­phide may be noted.

Research has also been done in the area of modified~tmosphere packaging. When normal or high pH porkIS stored at O°C in a gas atmosphere of 100% carbondioxide, the growth of some types of bacteria isprevented. Under these conditions spoilage of porkdoes not occur before four to five weeks. However, at

Can. lnsf. Food Sci. Technol. J. Vol. 23. No. I. 1990

lower concentrations of carbon dioxide or at highertemperatures the gas may not be as effective.

In all cases the shelf-life is based on the use of a goodoxygen barrier film containing saran or PVDC.

NOTE: Require 1 liter of 100% carbon dioxide per kgof meat in order to have sufficient residual gas in theheadspace to maximize shelf-life

PoultryThe poultry industry continues to be a growing area

for modified atmosphere packaging. Whole birds or cutup parts are packaged in a barrier pouch and then gas­flushed with carbon dioxide. The presence of carbondioxide selectively limits more objectional proteolysisof off-odor causing organisms while encouraging lactic­acid producing types. This method offers a tremendousincrease in shelf-life from a previous 7 to 9 days to 18to 21 days.

Since standard refrigeration can be used, there is noice and water spillage and transportation payloads canbe increased by 20 to 25% over ice-pack product. Thedry-pack method also allows the mixing of shipments,both in refrigerated transport and in warehouses.

Processed MeatsVacuum packaging is used almost universally for

packaging processed meat. Product stability is depen­dent upon minimizing color change, preventing oxida­tive off-flavours and suppressing microbial growth, allof which depend on the exclusion of oxygen.

Cured meat products are considered reasonably sta­ble due to the presence of microbial inhibitors suchas salt and nitrite coupled with the effects of heatprocessing. Most packaging systems that simplyexclude oxygen result in comparable product stabilityto gas packaging. Vacuum packaging has remainedmost popular because it not only removes oxygen butis also obvious when the vacuum is lost.

The major concern for maximizing product stabilityis the vacuum achieved and the oxygen barrier proper­ties of the film. Generally a good barrier film incorporat­ing saran should result in a shelf-life of 50 to 60 daysat 4°C.

Color Changes in Fresh and Processed MeatsColor is an important marketing tool, therefore any

evidence of off-colors or color fade can be critical atthe retail end. Due to extended shelf-life throughvacuum packaging and longer distribution chains, thishas become an increasing area of concern.

Some of the major factors affecting the appearanceof fresh and processed meats are light, temperature,oxygen, preservatives and bacterial spoilage.

LightStrong lighting can cause considerable product

deterioration, especially in the presence of oxygenaround fat-containing food. It appears to be mainly theshorter (ultra-violet) wavelengths in the light spectrum

AT /23

Page 3: Packaging and Meat Quality

·°2myoglObin.., ~ ~ oxymyoglobin

(PurPI\\ -02 !bri9ht red)

metmyoglobin

(grey ish-brown)

Table 1. Film Properties.

Polymers 02 T.R.

EVOH 0.5PVDC 5Nylon 40Poly Vinyl Chloride 125Polyester 70Polypropylene 3,000Polyethylene (4% EVA) 8,000Surlyn 5,400

02T.R. measured in cclm2/24 hr @ 23°C dry.M.V.T.R. measured in glm 2/24 hr @ 38°C. 90% R.H.

M.V.T.R.

334

2954818112527

that influence food quality because they promote theoxidation of fat and bleach colours. Lighting intensityis also an important factor since certain types of light(i.e., fluorescent vs incandescent) will emit differentintensities of light.

In order to minimize the effect of light it is impor­tant to package in a high barrier film, however it shouldbe noted that only opaque films will act as a total blockto light. Light actually accelerates the oxidation processand acts on the oxygen being transmitted through thepackage walls as well as the oxygen already in thepackage. Therefore, a good barrier film will limit theamount of oxygen in the package and consequentlylight will have less of a destructive effect.

TemperatureMeat colour stability is greatly affected by storage

temperature. Lower storage display temperatures (30- 32° F) tend to depress enzyme activity and minimizecolour changes. In general, temperature control is veryimportant in limiting rates of both undesirable chem­ical reactions associated with discoloration andspoilage reactions by growth of micro-organisms.

OxygenOxygen exposure is a critical element in the colour sta­

bility of meat. In order to give some background onthe effect of oxygen on meat pigments a reference charthas been attached (Figure 1).

The chief muscle pigment in red meat is a proteincalled myoglobin. Myoglobin is purple in colour butwhen exposed to oxygen it changes to oxymyoglobinwhich has a bright red colour. Thus when fresh meatis first cut it is purple in colour but its surface quicklybecomes bright red upon exposure to air. The desira­ble red of oxymyoglobin is not oxidation. It can shiftto metmyoglobin which has a brownish colour. Met­myoglobin is considered an unstable state and at thisstage may not be reversible back to the red oxy­myoglobin state.

PreservativesAnti-oxidants are used to help develop and stabilize

colour development in processed meats. The most fre-

24/ AT

quently used compounds are sodium ascorbate orsodium erythorbate. Ascorbate or erythorbate acceler­ate the conversion of metmyoglobin and nitrite tomyoglobin and nitric oxide and suppress the reversereaction. This results in a more complete conversionof the muscle pigment to the cured pigment form.

Bacterial SpoilageBacterial growth can contribute to colour deteriora­

tion of fresh meat. At lower numbers, micro-organismsare not strong promoters of discoloration. However athigh numbers, they do contribute to oxidative condi­tions that encourage discoloration. It is advisable tokeep refrigerated display temperature below 40°F inorder to retard microbial growth.

Choosing the Right Packaging FilmWhen choosing the appropriate packaging film the

following factors should be considered.1. Gas barrier properties. Does the product requirea barrier film or a permeable film to gases?2. Moisture barrier properties. Is the product sensi­tive to moisture pick-up?Is a high moisture barrier required?3. Anti-fog properties. Certain products such as freshpasta and some sausage products held refrigerated maycause fogging on film surface.Films are now available with anti-fog agents.4. Machinability. Depending on the machine certainfilm properties may be required.Slip/hot tack/high melt flow/stiffness etc.5. Mechanical strength. Film must be able to with­stand normal shipping/handling abuse.6. Sealability. Must be able to seal at normal produc­tion speeds.7. Economy. Protection versus cost.

See Table 1 and Table 2.

Factors Which Affect Oxygen Transmission RateIt has been found that the rate of oxygen diffusion

plays a key role in determining whether the conditionsnecessary for prolonged storage life are established andmaintained. As the oxygen transmission rate of pack-

J. InSl. Can. Sci. Technol. A/imenr. Vol. 23, No. I, 1990

Page 4: Packaging and Meat Quality

aging films increases, the storage life of the meat con­tained decreases.

3. TemperatureOxygen transmission rate is normally measured ata test temperature in the range of 20 to 25°C.However, such data do not indicate the performanceof a film at O°C, the recommended storage temper­ature for vacuum packaged meat. As storage tem­perature decreases so does the oxygen transmissionrate. At O°C oxygen transmission rate values aregenerally less than 10% of those at 25°C.

4. Relative HumidityThe oxygen transmission rate of films containingnylon or EVOH are influenced by the relativehumidity conditions under which the films are held.Humidity has a marked effect on transmission rateas you near 100% R.H.

2. ThicknessThickness of the barrier layer has a direct relation­ship to transmission rate. The thicker the nylon layeror PVDC coating the better the oxygen barrier. Thiswill also relate to any variation in thickness with aparticular structure.

Conclusion

In conclusion the particular requirements of specificmeat products need to be adequately understoodbefore decisions are made on which packaging optionto adopt. The requirements will depend on both thenature of the meat (fresh/processed) and the primarypurpose of the package.

Clarity and abrasionresistance

Clarity and abrasionresistance

Emulsion coating whichprovides oxygen barrierproperties

Inner layer Low density polyetylene Sealable layeror Surlyn

Middle layer Saran Coating

Emulsion coating whichprovides oxygen barrierproperties

Inner layer Low density polyetylene Sealable layeror Surlyn

Middle layer Saran Coating

Table 2. Typical barrier laminate.

Non-forming web

Outer layer Mylar (Polyester)

Forming web

Outer layer Nylon

1. CompositionThe basic and most commonly used gas barriers inmost structures are either nylon or polyester. Bothfilm types perform well in most commercial appli­cations. However, higher gas barriers structures maybe obtained by the addition of polyvinylidene chlo­ride (PVDC) or ethyl vinyl alcohol (EVOH). Thesebarrier materials substantially reduce the oxygentransmission rate but in turn increase costs.

Can. Ins!. Food Sci. Techno!. J. Vol. 23, No. I. 1990 AT I 25